Host-Specific Code

S-functions (system-functions) allow you to extend the capabilities
of the MATLAB environment by creating custom blocks. An S-function is
a computer language description of a Simulink® block written in MATLAB,
C, C++, or Fortran. C, C++, and Fortran S-functions are compiled as MEX
files, dynamically linked subroutines that the MATLAB interpreter
can automatically load and execute.